In an image display device such as a liquid crystal display device, an image forming system thereof essentially requires arranging a polarizing plate on each side of a glass substrate forming a surface of a liquid crystal panel. Typically, as the polarizing plate, a laminate is used which is obtained by laminating a transparent, polarizing plate protection film using triacetylcellulose or the like, to one or each of opposite surfaces of a polarizing film comprising a polyvinyl alcohol-based film and a dichroic material such as iodine, through a polyvinyl alcohol-based adhesive.
Generally, in an operation of attaching the polarizing film to a liquid crystal cell or the like, a pressure-sensitive adhesive is used. Further, in many cases, the pressure-sensitive adhesive is preliminarily provided on one surface of the polarizing film as a pressure-sensitive adhesive layer, because it has an advantage, for example, of being able to instantly fix the polarizing film to a liquid crystal cell or the like, and eliminate a need for a drying step to fix the polarizing film to a liquid crystal cell or the like. That is, in the polarizing plate attaching operation, it is common to use a polarizing plate with a pressure-sensitive adhesive layer.
Properties required for the pressure-sensitive adhesive layer include high durability free from aging deterioration of pressure-sensitive adhesion, and a capability of allowing the polarizing film to be peeled and re-laminated with respect to a surface of a liquid crystal panel even in cased where, during an operation of laminating the polarizing film to a liquid crystal cell, an error in lamination position occurs, or a foreign substance gets between laminated surfaces (reworkability).
Meanwhile, recent years, in an image display device for mobile applications such as a mobile phone, the entire module tends to be reduced in thickness and weight, particularly, in view of aesthetic design and portability. Thus, regarding an optical film such as a polarizing plate for use in an image display device, further thickness reduction and weight reduction are desired. Further, a usage environment such as usage in an outdoor harsh environment is becoming more diversified, and there is also a growing need for higher durability than ever before. In such a situation, there is a need for a polarizing film having a reduced thickness and excellent optical properties
As technical means for responding to the request for thickness reduction, there has been proposed a technique of providing a pressure-sensitive adhesive directly on a polarizing film, while omitting a protection film which has heretofore been given to the polarizing film.
For example, JP 2010-44211A (Patent Document 1) relates to an invention intended to provide a polarizing plate comprising a polarizing film having excellent durability even in high-temperature environments, and a pressure-sensitive adhesive layer provided on one of opposite surfaces of the polarizing film, and discloses a polarizing plate which comprises: a polarizing film; a pressure-sensitive adhesive layer provided on one surface of the polarizing film; wherein a pressure-sensitive adhesive constituting the pressure-sensitive adhesive layer has a storage elastic modulus (G′) at 23° C. of 0.2 to 10 MPa, and the pressure-sensitive adhesive layer has a thickness of 2 μm to less than 25 μm; and a protection layer composed of a transparent resin film and provided on the other surface of the polarizing film.
JP 2009-251177A (Patent Document 2) relates to an invention intended to provide a pressure-sensitive adhesion type polarizing plate comprising a polarizing film, a transparent protection film on only one surface of the polarizing film, and a pressure-sensitive adhesive layer on the surface of the polarizing film, wherein it is capable of satisfying a pressure-sensitive adhesion property as a pressure-sensitive adhesion type polarizing plate, and facilitating reworking without occurrence of break, and discloses a pressure-sensitive adhesion type polarizing plate which comprises a polarizing film, a transparent protection film provided on only one surface of the polarizing film through an adhesive layer, and a curable pressure-sensitive adhesive layer provided on the other surface of the polarizing film.